The present invention relates to a heat exchanger, and more particularly to a heat exchanger preferably used as an evaporator of a supercritical refrigeration cycle in which a supercritical refrigerant, such as CO2 (carbon dioxide), is used.
Herein and in the appended claims, the term “supercritical refrigeration cycle” means a refrigeration cycle in which refrigerant on the high-pressure side is in a supercritical state; i.e., assumes a pressure in excess of a critical pressure. The term “supercritical refrigerant” means a refrigerant used in a supercritical refrigeration cycle. Further, herein and in the appended claims, the upper, lower, left-hand, and right-hand sides of FIGS. 1 and 2 will be referred to as “upper,” “lower,” “left,” and “right,” respectively; and the downstream side of flow (represented by arrow X in FIGS. 1 and 10) of air through air-passing clearances between adjacent heat exchange tubes will be referred to as the “front,” and the opposite side as the “rear.”
The present applicant has proposed a heat exchanger used for use in a supercritical refrigeration cycle (Japanese Patent Application Laid-Open (kokai) No. 2005-326135). The proposed heat exchanger includes upper and lower header tanks disposed apart from each other; and a plurality of heat exchange tubes disposed in parallel between the two header tanks and having opposite end portions connected to the respective header tanks. Each of the head tanks is configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers. Each of the outside plates of the upper and lower header tanks has at least one an outwardly bulging portion extending in the longitudinal direction thereof and having an opening closed by the intermediate plate. The inside plate has a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along the longitudinal direction thereof. The intermediate plate has a plurality of communication holes in the form of through-holes so as to allow the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate. Opposite end portions of the heat exchange tubes are inserted through the respective tube insertion holes of the inside plates of the two header tanks and are brazed to the inside plates. At least one outwardly bulging portion of each of the upper and lower header tanks serves a refrigerant-passage outwardly bulging portion within which refrigerant flows in the longitudinal direction. The communication holes of the intermediate plate communicating with the refrigerant-passage outwardly bulging portion are connected by means of communication portions each formed between adjacent communication holes of the intermediate plate. The communication holes communicating with the refrigerant-passage outwardly bulging portion and the communication portions connecting these communication holes cooperate to form a refrigerant passage which communicates with the interior of the refrigerant-passage outwardly bulging portion and causes the refrigerant to flow along the longitudinal direction of the refrigerant-passage outwardly bulging portion. The widths of the communication portions are adjusted so as to change the cross sectional area of the refrigerant passage along the longitudinal direction.
In the heat exchanger disposed in the publication, since the cross sectional area of the refrigerant passage, which communicates with the interior of the refrigerant-passage outwardly bulging portion and causes refrigerant to flow along the longitudinal direction of the refrigerant-passage outwardly bulging portion, is changed along the longitudinal direction, the quantity of refrigerant flowing through respective portions of the refrigerant passage can be changed arbitrarily. Therefore, the refrigerant flow amounts of all the heat exchange tubes can be properly set so as to increase the heat exchange performance. In addition, the distribution of refrigerant to each heat exchange tube can be adjusted in accordance with the velocity distribution of air passing through air-passing clearances between adjacent heat exchange tubes.
However, since the degree of drift of refrigerant at the time of distribution to each heat exchange tube changes depending on the size of the heat exchange core section of the heat exchanger, in particular, the number of the heat exchange tubes, the widths of the communication portions, which constitute the refrigerant passage, must be optimally set in accordance with the number of heat exchange tubes communicating with the interior of the refrigerant-passage outwardly bulging portion.